Reliable anchoring is an important requirement for all kinds of water vessels, in particular rafts, boats, and ships, but also floating platforms and other semi-stationary objects. If one or more anchors come loose, significant damage can result to the water vessel, other water vessels, and/or crew, passengers etc.
Various methods for anchor monitoring have therefore been suggested.
U.S. Pat. No. 4,912,464 suggests an alarm system comprising a motion sensor connected to an anchor, and configured to monitor a motion signal produced by said motion sensor and raise an alarm under certain conditions, in particular when an acceleration above a threshold occurs.
U.S. Patent Application Publication No. 2003/0128138 A1 discloses a device that generates an alarm when a condition at an anchor or an anchor chain exceeds a set value, in particular when a jerk exceeds a predetermined measure, or when a predetermined force is exceeded.
DE 100 64 419 A1 discloses a movement or inclination monitoring device that has two or more base bodies, such as an anchor and its chain, that are directly or indirect connected, and two or more measurement elements that are used for continuous measurement of the acceleration of one or more base bodies, measurement of angles α of the base body axes relative to the gravitational force vector, a rotation β around a body axis, or a rate of rotation relative to α and/or β. The measurement elements are linked by cable or in a wireless manner. If a variation in acceleration, angle, rotation angle, or rotational velocity exceeds a predetermined threshold, an alarm signal may be displayed.
DE 38 10 084 A1 describes an alarm device which indicates the breaking loose or slippage of an anchor, said alarm having a position encoder (displacement sensor) which is connected to the anchor and rests with a wheel on the anchor (holding) ground and transmits the breaking away or slippage of the anchor to a signaling device present in the water craft via a pulse generator and a transmission device, such as a cable or in a wireless fashion, e.g., by ultrasound.
However, the quantities measured in the state of the art do not correlate optimally with a displacement of an anchor, and thus, in particular, do not correlate optimally with a reliability of the anchoring. In particular, anchoring may remain reliable if very high forces or jerks occur: the anchor may remain at least essentially stationary under such conditions. Under such conditions, state of the art devices may trigger false alarms. On the other hand, if an anchor has never made firm contact with the ground, both boat and anchor may slowly drift, and the anchor may thus be significantly displaced, without large forces or jerks occurring on the anchor or anchor chain, or without wheels or other rotatable elements attached to the anchor being rotated. Such situations may thus go undetected with the methods and devices according to the state of the art as described above.